Treatment of wax



\g, 1942- s. w. FERRIS TREATMENT oF-mx June 23 2 Sheets-Sheet 2 Filed Jan. 30, 1935 Patented June 23, 1942 3 UNITED STATES "PATENT osmos- TREATMENT OF WAX Seymour W. Ferris, Aldan lai, assignor to The Atlantic Refining Company, Philadelphia, Pa.,

a corporation of Pennsylvania ApplicationJanuary 30, 1935, Serial No. 4,157

9- Claims. (01. 196-18) The present invention relates to a processfor the separation of solid or semi-solid waxy constituents from hydrocarbon oils and/or the separation of wax constituents from-one another, and" relates more particularly to the separation of wax from petroleumcrude oils, and distillates and residuums thereof.

A principal object of my invention is to effect a completeness of separation with an economy not heretofore attainable in the employment of conventional processes or combinations of processes for the separation of wax from oil.

A further object of my invention is to effect, by a single general procedure, varying degrees and kinds of separation of hydrocarbon-oil-wax mixtures-witha likeeconomy. Thus, for example, I am able to separate from such mixtures, oils substantially'free ofwax or containing such definite amounts ofwax as to render them desirable commercial products; to separate from given wax-bearing oilseither one wax of specific phys-ica-l properties, or a series of waxes, each of specific but different physical properties; to simultaneously produce an oil substantially free from, or containing adefinite amount of wax, and a wax substantially f-ree'of oil; and finally, to produce from a given wax mixture, two or more waxes having properties difierent from each other and from the initial wax mixture.

My invention is characterized not only by the ability to accomplish in a single procedure, a degree ofseparation heretofore requiring a combinaticn of -processes,-or the repetition of a single process, but also by its applicability to a greater variety of wax-bearing oilsthan any one of the conventional methods employed for sep- ;aration purposes.

Light lubricatingoilsand paraffin waxes have ybeen commonly produced from paraflin distillate by the well-known steps of chilling, pressing and sweating; and heavy lubricating oils and petrolatum stocks have been produced from residuums and heavy wax-bearing distillates by dilution with asolvent more volatile than the ;,stock, chilling, separation of the solids and/or semi-solids by settling, centrifuging or filter pressing, and removal of the solvent by distilla- Qtion. The crude petrolatum stocks soseparated tcontain-considerable quantities-of oil which cannot be separatedby sweating. The normal pro- .cedure for the furtherseparation of oil from such stocks", comparatively inefiective and rarely practiced-because o'f its high cost, has'been a qrepetition of the process employed-on theorigi- :Fnal stock. *Iritermediatabetween these tw yp of wax-bearing stocks are others medium in viscosity and boiling range, which are not amenable to treatment by'either of the procedures described. My process is applicable to substantially the entire range of wax-bearing oils and I am able to effect not only the primar separation of the oil and wax, but also, if desirable, a fractionation of the wax.

' The processes for the separation of wax and oil commonly employed in the petroleum industry all result in an initial separation of a wax contaminated withrelatively large percentages of) oil. The slack wax" obtained by-filter pressing chilled paraffin distillate usually contains from 25% to 55% of oil; and the crude petrolatum stocks obtained by centrifuging or cold settling naphtha dilutedmotor oil stocks, cylinder stocks or crude residuums all contain upwards of--25% ofoil. The same is true of the wax cakesobt-ained by the filter pressing methods employed in removing the precipitatedwax from the diluted oil solutions in the more recent processes employing propane, mixtures of hen-- zcl-and acetone and other diluents. While the waxes from parafiin distillate may be freed of oil by the well-known sweating process, the petrolatumstocks and filter press cakes from stocks other than paraiiin distillate can only be rendered oil-freehy elaborate procedures not generally practiced because of the disparity between the cost. of such methods and the commercial value of the wax produced.

I have found that, contrary to general belief and statements in the literature, the .wax precipitated by chilling waxebearing hydrocarbon oils-either as such or indilution in various solvents, is in itself pure wax containing no ,oil, and I have further. discovered .a general procedure and modifications thereof ,.described hereinafter, wherebytheoil .adhering to the surfaces of theindividualwaxlcrystals or contained in the interstices between. the. crystals may be either removed substantially; completely or to an extent not hitherto practically and economically possible, by.,-a displacingand washing operation following the. crystallization of the. wax from the mother jliquor, i. .e., from the original or the diluted :hydrocarbon L011- .IHerein, the term .crystalline wax,;when emlployed,isttolbe understoodto'include any and all .types ,of. solid and/tor semi-solid waxy hydrocarbons, whether of distinctly crystalline type or of theso-called amorphous orpmal-crystalline type.

"Suchtermisto be UIIdBIStOQdLtO include, for example, .waxy materials. ,obtainable from; DQ1313 distillates, intermediate distillates, high viscosity distillates and/or residuums.

Briefly, the several steps of my process are:

(1) The preparation by any known method, for example by distillation or by blending, of a wax-bearing stock of such relative concentration of oil and wax that upon being cooled to the desired separating temperature, wax will crystallize in a quantity not more than substantially by volume of the oil-wax mixture, or by dilution of a given wax-bearing stock with any suitable solvent, so that upon cooling to the desired separating temperature, not more than 10% by volume of wax will crystallize.

(2) The cooling of the stock or diluted stock to the desired separation temperature, with or without agitation, in such a manner as to effect a dispersion of the wax crystals thruout the mother liquor with reasonable uniformity. If agitation is resorted to, the cooled mother liquor containing the wax crystals is thereafter preferably permitted to stand, unagitated, for sufficient time to effect the formation of a highly porous wax mass, the structure of which has appreciable mechanical strength or cohesion, such mass containing not more than substantially 10% of crystalline wax per unit volume of the mass.

(3) The displacement of the mother liquor from the chilled wax mass by a displacing or washing liquid, preferably an oil solvent, without substantial agitation and under a low differential pressure, in such a manner that a substantially horizontal interface is maintained between the mother liquor and the washing liquid, with suitable gravity differential between the mother liquor and the washing liquid contributing substantially to the maintenance of such horizontal interface.

(4) The recovery of the wax, and the separation of the oil from the solvent and/or displacing liquid resulting from the third step of my process.

An important feature in the successful operation of my process and the various modifications thereof i the limitation of the volume occupied by the wax crystals in the wax mass during the removal of the mother liquor from such mass. To this end, careful adjustment of the concentration of wax in the mother liquor, the gravity differentials between wax, mother liquor and displacing liquid, and/or the differential pressures employed in the displacement, is expedient.

In carrying out my process, it is necessary to control the quantity of wax in the mother liquor so that the crystalline wax content of the mass resulting from the chilling of the mother liquor will not exceed substantially 10% of any unit volume of the mass at the beginning of the displacing operation. In most instances, it has been found that the crystalline wax contained in the wax mass at the beginning of the displacement step should be of the order of from 1% to 6% by volume, and preferably of the order of from 2.5% to 4.5% by volume; it may, however, be as high as substantially 10% by volume depending upon the character of the wax crys-' tals, harder and larger crystals tending to permit higher wax concentrations. Should the crystalline wax content of the mass exceed substantially 10% by volume of said wax mass from which the mother liquor is to be displaced, the wax particles will be'so compacted together that the passages between them filled with mother liquor will be too restricted to permit the displacement of mother liquor at the preferred low differential pressures. However, during the displacement and/or washing operation, some compacting of the wax crystals is to be expected, and at the completion of the said operation the concentration of crystalline wax in the washed wax mass may be of the order of 20% by volume, depending upon the degree of compacting caused by the displacement step. If the concentration of wax in the mass is so great as to render the mass too dense, it will be necessary to employ an undesirably high differential pressure to effect displacement of mother liquor from the mass, with the result that the displacing liquid will tend to flow more rapidly through any cracks or areas of low wax content than through the main body of the wax mass, thereby causing unequal displacement of the mother liquor and yielding a final wax product containing residual oil. By maintaining a low concentration of wax, the pressure required to cause the displacing liquid to pass through the wax mass is low; and when a wash liquid of different specific gravity than that of the mother liquor is used, the tendency of the displacing liquid to flow more rapidly through areas of low wax content is checked by the tendency of the mother liquor to maintain a substantially horizontal interface. Thus, when displacement is downward and the displacing liquid is of lower gravity than the mother liquor, if a vertical crack occurs, the displacing liquid tends to fill that fissure and thus extend a column of liquid below the interface. However, the heavier mother liquor, which must be forced from the fissure, resists the entrance of the displacing liquid and tends to force it back and maintain a substantially horizontal interface between the two liquids. Since the gravity differential between the two liquids is necessarily limited, this tendency to maintain a horizontal interface is effective only against relatively low displacing pressures. Hence, if the crystalline wax content of the mass is so great as to require high differential pressures, any cracks in the cake will become enlarged, gravity differentials between the liquids will lose their significance, the interface between the displacing liquid and the mother liquor will be disrupted, and washing of the wax mass will be incomplete. Furthermore, the compacting effect of high differential pressures is undesirable in that the rate of displacement and washing is materially reduced. However, in accordance with my invention, the employment of a relatively porous wax mass and relatively small differential pressures permits a reasonably rapid displacement of mother liquor and a very complete washing of residual liquor from the wax mass.

My invention is differentiated from known processes, particularly filter press operations, in that at no time during the removal of the mother liquor from the wax crystals is any part of the crystalline mass still containing appreciable quantities of mother liquor compacted to a crystalline wax concentration greater than 20 parts by volume, and that, in general, at no time does the differential pressure required in effecting displacement exceed substantially 5 lbs/sq. in. per unit (1 foot) depth of the wax mass, and usually at the outset does not exceed 2 lbs/sq. in. It is to be understood, however, that at some stage of the operation and particularly during the latter part thereof, the pressure may be somewhat in excess of 5 lbs/sq. in. In many instances, throughout the major portion of the-disp1acing step, pressures are less than 2 lbs/sq. in. For

example, if the displacing liquid be above the wax mass, in suitable apparatus, the static head of the displacing liquid (or less if the effluent liquid be taken through a throttle valve) is usually sufficient tocarry out a major portion of the displacement.

On the contrary, in conventional. filter press operations, the press cake contains of the order of from 50% to 75% of crystalline wax. Pressures required to effect washing in conventional filter press operation, are usually in excess. of 30 lbs/sq. in. for a cake thickness of the order of from 1 1 to 3. inches; and the resulting washed cakes. contain upward of. 25% of oil. It is characteristic of filter press operation that the compact nature of the wax. cake formed offers such resistance to the flow of liquid therethrough as tonecessitate the building up of a large number of thin cakes during filtering. My invention is further contrasted with such operation in. that the extremely porous nature of the wax. mass or body permits satisfactory and substantially complete removal of oil from a wax mass many times the thickness of the normal filter cake, so that in the process of my invention, a relatively small number of large masses of wax may be handled. While filter cakes are limited to thicknessesof the order of from 1 to 3 inches, my process is applicable to wax masses, one foot or more, and preferably on the order of 5 feet or even greater, in depth.

My process may be further distinguished from conventional filter pressing in that both the main portion of the mother liquor and the residual portion normally remaining in the wax mass at the completion of the filtering step, may be removed substantially completely in one opera tion.

In accordance with my invention, a variety of solvents and displacing or washing liquids, or combinations thereof, may be employed. It is essential for the economical operation of my process, that the crystallizing liquid or mother liquor be prevented from admixing to substantial extent with the displacing or washing liquid. This may be accomplished, for the major part, by maintaining a sufficient gravity differential between the mother liquor and the displacing liquid. If the displacement of the mother liquor from the wax mass is to take place downwardly, it is preferable that the displacing liquid have a lower specific gravity than the mother liquor, whereas, if the displacement is to be effected upwardly, it is preferable that the displacing liquid have a higher specific gravity than the mother liquor. By maintaining a suitable gravity differential, properly coordinated with respect to the direction of fiow during displacement, it is possible to obtain a substantially horizontal interface between the motor liquor and the displacing liquid. From the economical viewpoint, it is highly desirable to prevent substantial disruption of the interface, inasmuch as the admixing of mother liquor and displacing liquid would necessitate the employment of considerably more displacing or washing liquid to produce the desired degree of oil removal. Therefore it is necessary that no substantial agitation take place during the displacement or washing operation.

Furthermore, I find that my process may be operated most advantageously if the specific gravities of the wax, the mother liquor and the displacing liquid be substantially different. For

example, ifdownward displacement is to be efof the mother liquor be highest and that of the displacing liquid be lowest, while the gravity of the wax be intermediate but preferably approaching that of the displacing liquid. In this instance, the relatively heavy mother liquor will exert a considerable buoyancy upon the crystals of the wax mass, thereby aiding inthe maintenance of the uniformity and porosity of the wax mass. During the downward displacement and/or washing, if the gravity of the displacing liquid is less than" that of the mother liquor, and less than but approaching that of the wax, there will be less tendency for the wax to settle or compact upon passage of the displacing liquid thru the wax mass, than if the displacing liquid were of markedly lower gravity than the wax, and at the same time a relatively uniform interface may be maintained between the displacing liquid and the mother liquor.

On the other hand, if upward displacement is to be effected, it is desirable that the specific gravity of the mother liquor be lowest and that of the displacing liquid be highest, while the gravity of the wax be intermediate, but preferably approaching that of the displacing liquid. In this case, the relatively light mother liquor will exert little buoyancy upon the crystals of the wax mass, thus permitting a certain degree of settling of the wax against the upward fiow of heavy displacing liquid, thereby aiding in the maintenance of a porous wax mass. During upward displacement, if the gravity of the displacing liquid is greater than that of the mother liquor and greater than but approaching that of the wax, there will be less tendency for the wax to compact upwardly upon passage of the displacing liquid thru the wax mass than if thedisplacing liquid has a markedly greater gravity than that of the wax, and at the same time a relatively uniform interface may be maintained between the displacing liquid and the mother liquor.

When solvents are employed in making up the crystalliaing solution or mother liquor, they of one from the other at the end of the opera-- tion may be readily eifected, for example by distillation.

While I do not intend to confine myself to any one or several specific procedures for carrying out my process, the following exampleswill serve to illustrate the general principles of my invention.

Referring to Fig. l of the drawings, which illustrates apparatus suitable for carrying out the separation of oil-wax mixtures by downward displacement:

From a steam jacketed stock tank 5, 40 parts, for example, of a wax bearing distillate from East Texas crude oil having a pour test of F., and a Saybolt Universal viscosity of 60 seconds at 210 F., is Withdrawn through valve-controlled pipe 2 and pumped by pump 3 through valve-- controlled pipe 4 into a mixing tank 5 provided with heating coilB and stirrer I. Simultaneously or subsequently 60 parts, for example, of ethylene dichloride is withdrawn from solvent tank 8 by means of valve-controlled pipe 9 and pumped by pump Ill through valve-controlled pipe 4 into mixing tank 5. Herein the solvent and distillate containing wax are agitated at a temperature of, for example, 120 F., until a homogeneous solution is obtained. The resulting solution is passed from the mixing tank 5 by means of valve-controlled pipe II and is pumped by pump l2 thru valve-controlled pipe l3 to chilling device I4, wherein the solution is cooled until the temperature is, for example, of the order of 85 F., and a portion of the Wax has crystallized. This oil-wax-solvent mixture is passed from the chiller 14 by means of valvecontrolled pipe l5 into the brine-jacketed displacement tower Hi, above the screen 11. Prior to the introduction of the chilled mixture into the tower l6, air pressure is applied to brine tank l8 through valve-controlled pipe l9 provided with a valved vent Na, and brine of a specific gravity greater than that of the chilled mixture, is forced through valve-controlled pipe 20 and pipe 2| into the conical lower section of tower l6 until it barely covers the screen 11. The brine and screen ll thus support the chilled oil-wax-solvent mixture in the tower IS. The mixture contained in the displacement tower I6 is then cooled at a rate of, for example, 1 F. to 4 F. per hour, until the temperature of the mixture is of the order of, for example, 65 F., and the desired final quantity of wax has crystallized out. The cooling in the tower I6 may be effected by circulation of cold brine in the tower jacket and/or by the employment of brine coils or pipes (not shown) installed within the tower.

The mixture is preferably allowed to remain in a quiescent state within tower I6 during the final cooling period, in which time the wax crystals form an agglomerate mass of appreciable mechanical strength while still retaining a high degree of free space or porosity thruout which the mother liquor is distributed. At the completion of the cooling period, 100 parts of a displacing liquid, for example, naphtha of 50'A. P. I. gravity, is passed from the displacement liquid tank 22 through valve-controlled pipe 23, cooled to about 65 F. in cooling coil 24 and introduced into the displacement tower l6, by means of valve-controlled pipe 25, above the surface of the chilled oil-wax-solvent mixture contained therein. The displacing liquid is introduced in such a manner as to prevent substantial disturbance of the wax mass from which the oil and solvent are to be displaced. Preferably simultaneously with the introduction of the displacing liquid at the top of tower I6, brine is withdrawn from the bottom of said tower and returned to the brine tank ill by means of valvecontrolled pipe 20. Oil and solvent from the wax mass, displaced downwardly by the incoming displacing liquid, is withdrawn from the bot tom of tower l6 and passed through valve=con=- trolled pipes 26 and 21 into receiving or heavy efilux tank 28. If necessary Or desirable in order to expedite displacement, after introduction of the displacing liquid into tower l6, slight pressure may be applied to the tower, above the level of its contents, by means of valve-controlled air line 29 provided with valved vent 30. The differential or displacement pressure should Preferably be maintained at less than 5 lbs/sq. in. per 1 foot depth of the wax mass, in order to prevent undue compacting of the wax crystals and/or distortion of the interface between the mother liquor and the displacing liquid. When substantially all of the oil and solvent (heavy efilux) has been displaced from the wax mass into receiving tank 28, as evidenced by a marked change in gravity or other critical property of the liquid issuing from the tower IS, the liquid thereafter withdrawn from the tower is diverted into receiving or light efiiux tank 3| by closing valve-controlled pipe 21 and opening valve-controlled pipe 32. This light efflux will consist primarily of displacing liquid containing residual oil and solvent which has been washed from the Wax mass. The displacing or washing operation is preferably continued until the efiluent from tower I6 is principally displacing liquid.

At the completion of the displacing or Washing operation, the wax mass containing residual displacing liquid is forced upwardly and out of tower it through valve-controlled pipe 33 into wax receiving tank 34, by means of brine introduced into the bottom of the tower from brine tank [8. If necessary or desirable, the wax mass contained in tower l6 may be rendered more fluid by the application of steam in the jacket surrounding said tower. The heavy efilux (oil and solvent) in tank 28, the light efllux (oil, solvent and displacing liquid) in tank 3|, and the wax containing residual displacing liquid may be withdrawn from their respective receiving tanks by means of valve-controlled pipes 35, 3B and 31 and passed to distilling apparatus (not shown) wherein the solvent, i. e., ethylene dichloride, and the displacing liquid, i. e., naphtha, may be separated and recovered from the oil and wax.

While, in the above instance, I have described the chilling of the solution of oil stock and solvent from the mixing tank 5 as being effected partially in the chiller l4 and partially within the displacement tower I6, I may, if desired, pass the heated solution directly from the mixing vessel 5 to the tower It by means of valve-controlled by-pass 38, and effect such chilling entirely within the tower IE, or I may chill the solution entirely in the chiller I4 prior to the introduction thereof into the displacement tower H3. The latter method of operation may be carried out by pumping the heated solution directly from mixing vessel 5 through valve-controlled pipe I3, chiller l4, and valve-controlled pipe 15 into tower Hi. In this instance, the chilled mixture is preferably allowed to remain in a quiescent state within tower l6 for a period of, for example, 4 hours, during which time the crystals form an agglomerate mass having appreciable mechanical strength while still retaining a high degree of free space thruout which the mother liquor is distributed. Due to the gravity difierential between the wax and mother liquor a certain amount of upward settling of the former occurs, so that at the end of the quiescent period a lower layer of oil solution relatively free of crystalline wax is present, which may be of the order of 30% of the volume of the total charge. This layer is drawn off from the bottom and at the same time the wax mass settles until, upon completion of the removal of the oil solution, the bottom of the wax mass rests upon the screen. If desired, displacing liquid may be introduced above the chilled mixture contained in the tower, prior to the withdrawal of the layer of oil solution from the bottom thereof. The displacement-- step is then carried on as above described.

The following tables will serve to illustrate the results which may be obtained when operating in accordance with the general procedure described above. For brevity, the stocks treated in the examples will be defined as follows:

- Efiiux and East Texas Petrolatum Stock Heavy Efllux refer to stocks from which a portion of the wax has been removed by a previous displacement dewaxing treatment. It is to be understood that the examples given herein are merely for purposes of illustration, and that my invention is in no wise limited thereto but may be employed in the treatment of a wide variety of wax-bearing stocks from sources other than East Texas crude oil.

In the examples, hereinafter given, the grav- TABLE I Downward displacement ities expressed are to be understood to be A. P. I. gravities at 60 F. For instance, when the expression 89 naphtha is employed, it is to be understood to mean naphtha having an A. P. I. gravity (at 60 F.) of 89 degrees.

Exam le- Stock:

Source E. Texas int. E.Texaspiln. E. Texas pet. E. Texas int. E. T x pet,

dist. stock. dist. stock. Pour test 120 F 80 F 135 F 120 F 135 F, Solvent Ethylene di- 89 naphtha... Ethylene di- 89 naphtha... Butane.

chloride. chloride. Solution of stock+solvent:

Percent by volume of solvent.-- 60 87 85. Heat in mixer to 120 100 F 120 100 F 100 Method of chilling stock-solvent All outside of All withm dis- All outside of All outside of All outside 0 solution. dis p l a c plao. tower. d1s p l a c dis p l a c displac. towtower. tower. tower. er. Chilling:

Chilled to- Outside tower--. 65 F None 65 F 32 F 8 F, Within tower- None F None None None. Chilling rate F./hou.r):' v

Outside tower... 4 4 2.5. Within tower 8 Displacement:

Displaeing liquid Wax saturat- 89 naphtha." Wax saturat- 89 naphtha... Butane,

ed naphed 50 naphtha. the. V01. of displacing liquid used 36% 40% 44% 40% based on charge. Temp. of displacement F 32 F.. 65 F 32 F 8 F. Specific gravity of mother liquor 1.13 0. l. 23 0.73 0,65.

at displacing temperature. Viscosity of mother liquor at dis 2.1 0.67. 1.13 0.53 0.31,

placing temp. (centipoises). V Specific gravity of displacing 0.8..... 0.66 0.80 0.66 0.61.

liquid at displacing temp. Viscosity of displacing liquid at 0.8 0.32 0.8 0.32 0.24,

displacing temp. (centipoiscs) Products:

Wax-

Percent yield based on stock. 49.4. Per cent oil in wax 0.4. 1 Melting point of wax- 146 F. 1

Per cent yield based on stock 67. 7 50.6. Pour test F.-. 65 F 65 F 65 F.

TABLE II Downward dzsplacement Example- Stock: I

s rce E. Texas mt. E. Texas int. E. Texas 1nt. E. Texas int. E. Texa int,

dist. dist. dist. di Pour test 120 F 120 F 120 F 120 F. v solv nt 75% ethylene Ethylene di- 35% acetone; Ethylene div dichloride; dichloride. 65% benzol. chloride. 25% 88 naph. Solution of stock+solvent:

Percentbyvolume ofsolvent.... 55 60 60 60, Heat in mixer to F 118 F 110 E 118 F, Method of chilling stock-solvent Partial out- Partial out- Partlal out- Partial outsolutiou. side. Parside. Parside. Pardisplac. side. Partial inside ti a1 inside tial inside tower. tial inside displae. displac. displac. displac. tower, tower. tower. tower.

TABLE Downward displacement Example Chilling:

Chilled Outside tower 80 F. Within tower... 60 F. Chilling rate F.lhour):

Outside tower. 6. 6. Within tower 2. 5. Displacement:

Displacing liquid 88 naph Wtter white 88 naph Ether.

1s Vol. 01' displacing liquid used 35% 35%.

based on charge. Temp. of displacement F 60 F 60 F 60 F. Specific gravity of mother liquor 1.03 1.13 0.876 1. 13.

at displacing temperature. Viscosity of mother liquor at 2.4 2.2 1.6 2.2.

displacing temp. (centipoises) Specific gravity oi displacing 0. 643 0.813 0.643 0.72.

liquid at displacing temp. Viscosity of displacing liquid at 0.27 1. 05 0. 27 0. 24.

displacing temp. (centipoises). Products:

Wax-

Percent yield based on stock. Percent oil in wax Melting point of wax Percent yield based on stock.

Pour test TABLE III Downward dzsplacement Example- Stock:

Source E.'1exasp11n. E. Texas int. E.Texaspfin. E. Texas int. E. Texas et dist. 4060% by. efilux. dist. 60-80% dist. stock. cut. cut. Pour test 60 F 75 F 120 F 135 F. Solvent Ethylene dl- Ethylene di- Ethylene di- 35% acetone, Ethylene dichloride. chloride. chloride. benzol. chloride. Solution of stock+solvent:

Per cent by vol. of solvent 60 88. Heat in mixer to 83 F.. 76 F F )3. Method of chilling stock-solvent All outside of Partial out- Partial out- All out of dissolution: d i s pl a c side. Partial side. Partial plac. tower.

tower. inside disinside displac. tower.- plac. tower. Chilling:

Chilled to Outside tower 35 F 35 F 30 F 65 F. Within tower... None 0 F 0 F None. Chilling rate (F./hour):

Outsidetower 6.1 9.1 7.3 2.7. Inside tower 0.85 0.92 Displacement:

Displacing liquid Special naph- 88 naphtha... Special naph- 15% benzol, Special naph- I the. the. 85%acetone. tha. Vol. of displacing llqllld used 40% 47% 25% 77%.

based on charge. Temp. of displacement---.-- 35 F 0 F 0 F 65 F. Speciflcgravityofmotherliquor 1.13 1.23 1.20 1.24.

at displacing temperature. Viscosity of mother liquor at 2.0 3.0 2.8 1.1.

displacing temp (centipoises) Specific gravity of displacing 0.78 0.67 0.80 0.8.

liquid at displacing temp. Viscosity of displacing liquid at 1.03 0.40 1.6... 0,3,

displacing temp. (centipoises) Products:

Wax-

Per cent yield based on 2.7 7.6 14.9 8.1 26.6

stock. Per cent oilinwax 5-7 2.3 0.54 0.7 2.0. on Melting point of Wax 123 F 120 F 118 F 155 F 151 F. Per cent yield based on 97.3 92.4 86.7 91.9 73.4.

stock. Pour test TABLE IV Downward displacement Example Stock:

source E. Texas pet. E. Texas pet. E. Texas pet. E.Texaspffn. E. Texas int.

stock. stock by. stock by. dist. 60-80% dist. efllux. efliux. cut. Pour test F 75 F 120 F.

TABLE IV-Continued Downward displacement Example.

Solvent Ethyl ne di- Ethylene di- Ethylene d,i-, Eth .lene f chloride. chlorldc. chloride. chl olide. i ififglilg? d1 Solutlon i stock-l-solvent: l

Percent by voloof solyent. .80 39.5 J 87. 4 70 7 Heatin mixer to 90 F 95 F ng Method of chilling stock-solvent Partial out- Partial :out- All out-sideoi rd-rii'al out- Solutwnid B 1 d isp l a c s ide. Partlal lnslde tlal inside tower. t-ial inside g 0 disp lac.

O r. ower. Chilling: tower Ohilled-to-- Outside tower 70 F Within tower- Chilling rate F./hour):

Outside tower 7, Inside tower .i Disllgacelnentz l (1 88 llth 88 hth isp acing iqui D flP 88 a hthii... S eci lna vol. of displacing liquid used 45 132% "P itflfiffiif? 2 5 5? based on charge. Temp. of displacement 0 F 9 Specific gravity of mother liquor 1. 20 L 2 at displacing temperature. Viscosity of mother liquor at' 2,9 u 2 7 displacing temp. (centipoises) Specific gravity of displacing 0. so 1 1,

liquid at displacing temp. Viscosity of displacing liquid at 1. 6 0, 24,

displacing temp. (centipoises) Products:

Wax-

Bercent yield based on stock. i Percent oil in wax O1 Melting point of wax l ercent yield based on stock. Pourtesh,

Referring now to Fig. 2 of the drawings, which illustrate apparatus suitable for carrying out the separation of oil-wax mixtures by upward displacement:

From a steam jacketed stock tank I, parts, for example,..of an East Texas intermediate distillate, having a pour test of 120 F., is withdrawn through valve-controlled pipe 2', and pumped by pump 3' through valve-controlled pipe 4', into mixing tank 5', provided with heating coil 6 and stirrer ll. Simultaneously or subsequently 61' parts, for example, of ethylene dichloride is withdrawn from solvent tank 8' by means of valvecontrolled pipe 9, and pumped by pump ill through valve-controlled pipe l into mixing tank 5'. I-Ierein the solvent and distillate containing wax is agitated at a temperature of, -for example, 120 F., until a homogeneous solution is obtained. The resulting solution is passed from the mixing tank 5 by means of valve-c0ntrolled pipe H, and is pumped by pump l2 through a chilling device it, wherein the solution is cooled until the temperature is of the order of, for example, 65 and the desired quantity of wax has crystallized. This oil-waxsolvent mixture is passed from the chiller I4 by means of valve-controlled pipe l5, into the brine jacketed displacement tower it, up to the level of screen ll. The chilled mixture is allowed to remain in a quiescent state within tower Hi for a period of, for example, .6 hours, during which time the wax crystals form an agglomerate mass of appreciable mechanical strength while still retaining a high degree of free space or porosity. At the completion of the quiescent period, 50 parts of a displacing liquid, for example, ethylene dichloride, is passed from the displacementliquid tank 22' through valvecontrolled pipe 23, cooled .to about F. in cooling coil 24', and introduced into the displacement tower I6 by means of valve-controlled pipe 2-5, below the surface of the chilled oil-waxsolvent mixture contained therein. The displacing liquid is introduced in such a manner as to prevent substantial disturbance of the chilled mixture from which the oil and solvent are to be displaced. Oil and solvent from the wax mass, displaced upwardly by the incoming displacing liquid, is withdrawn from the top of tower l6 and passed through valve-controlled pipes 26' and .2 1, into receiving or light efiiux tank 28'. If necessary or desirable, in order to expedite displacement, slight pressure may be applied to the tower 16', .by introducing air, under pressure, above the displacement liquid in tank 22 by means of valve-controlled air line 29'. The differential or displacement pressure should preferably be maintained at less than 5 lbs/sq. in. per 1 foot depth of the wax mass, in order to prevent undue compacting of the wax crystals and/or distortion of the interface between the mother liquor and the displacing liquid. When substantially all of the oil and solvent (light efllux') has been displaced from the wax mass into receiving tank 28, as evidenced by a marked change in gravity or other critical property of the liquid issuing from the tower iii, the liquid thereafter withdrawn from the tower is diverted into receiving or heavy eillux tank 39' by closing valve controlled pipe 21 and opening valve-controlled pipe 3!. This heavy efllux will consist primarily of displacing liquid containing residual oil and solvent which has been washed from the wax mass. The displacing or washing operation is preferably continued until the ,efiiuent from the tower i5 is princi pally displacing liquid.

At the completion of the displacing or washing operation, the wax mass containing residual displacing liquid may be withdrawn from the bottom of tower 16 by means of valve-controlled pipe 2i, and passed to storage. Or, the wax mass may be heated, by circulating steam through the jacket of tower Hi, to render it sufficiently fluid to pass through the screen II to suitable storage. In this case, after the wax mass has been rendered fluid, air pressure is applied to brine tank [8 through valve-controlled pipe I9 provided with valved vent l9'a, and brine is forced through valve-controlled pipe. 20' and pipe 2| into the tower l6 beneath the wax and solvent contained therein. The fluid mixture is forced upwardly and out .of tower l6 through valve-controlled pipes 26' and 32 into wax receiving tank 33'. The light effiux (oil and solvent) in tank 28, the heavy efliux (oil, solvent and displacing liquid) in tank 30', and the wax containing residual displacing liquid may be withdrawn from controlled pipe l5 into tower 16. The displacement tower l6 may be provided with cooling means, preferably a plurality of vertical tubes (not shown), in addition to or in place of the brine jacket shown.

Instead of the cylindrical, straight walled displacement tower l6 shown in the drawings, I may employ a fully or partially tapered tower, for example such as disclosed in the co-pending application of J. A. Alexander, Serial No. 4158, filed January 30, 1935, now Patent No. 2,079,596. Such improved form of tower aids materially in preventing cracking and channeling of the wax mass during displacement.

The following table will serve to illustrate the results which may be obtained when operating in accordance with the general procedure described above.

TABLE V Upward displacement Example- Stock:

Source E. Texas int. E.'l xas pfin. E. Texas pffn. E.Texas pfin. E. Texas int.

dist. dlst. dist. dist. wax. Pour test 115 F 139 F. MP. olvent Ethylene d1- 89 naphtha... 89 naphtha 89 naphtha Ethylene dichloride. chloride, Solution of stock-l-solvent:

Per cent by vol. of solvent 80 65 6 65 90. Heat in mixer to 130 76 85 F 76 F 140 F. Method of chilling stock-solvent Partial out- All outside of All outside of All outside of All within disol ti side. Part al dis p l a c dis p l a c d is pl a c plac. tower.

inside dlS- tower. tower. tower. plac. tower. Chilling:

Chilled to Outside tower F 32 F None. Within tower 16 F None 90 F. Chilling rate (F./h0ur):

Outside tower Inside tower 1 Displacement:

Displacing liquid Ethylen (11- ate hlte Naphtha and Naphtha and Ethylene dichloride. st. nltrobennitrobenchloride.

zene. zene. Vol. of displacing liquid used 108% 30 based on charge. Temp. of displacement 16 F 32 F 32 F 32 F F. Specific gravity ofmotherhquor 1.24... 0- 3 0.73 0.73 1.22.

at displacing temperature. Viscosity of mother liquor at 0.8.

displacing temp. (eentipoises) Specific gravity of displacing 1.24.

liquid at displacing temp Viscosity of displacing l qu d at 0.75.

displacing temp. (centipolscs) Products:

Wax

Per cent yield based on 1 .7 -8 7.4 8.2 62.6.

stock. Per cent oil in wax 2-1 1.7 1.2 0.5. Melting point of wax Oil (or efllux wax):

Per cent yield based on 37.4 a

stock. Pour test 126 F. M. I.

their respective receiving tanks by means of valve-controlled pipes 34', 35, and 36, and passed to distilling apparatus wherein the solvent and the displacing liquid may be separated and recovered from the oil and wax.

While, in the above instance, I have described the chilling of the solution of oil stock and solvent from the mixing tank 5 as being effected entirely outside of the displacement tower I6, I may, if desired, effect such chilling partially in the chiller l4, and partially in the tower I8, or I may chill the solution entirely in the displacement tower !6'. The latter method of operation may be carried out by pumping the heated solution directly from mixing vessel 5 through valve-controlled by-pass 31' and valve- (not shown) .75 the volume of the mixture charged).

While the examples given above illustrate, in general, the results which may be obtained by displacement following a single crystallization of wax from solution, I may employ a series of two or more crystallizations, at successively lower temperatures, with the removal of crystallized wax after each chilling and displacement.

For example, 55 parts by volume of East Texas parafiin distillate were mixed with 45 parts by volume of ethylene dichloride, and heated with agitation, to about F., until substantially complete solution was obtained. The solution was then chilled to 63 F., passed into a displacing tower, and the mother liquor was displaced downwardly from the crystalline wax mass with 45 parts by volume of special naphtha (based on The resuiting wax, after removal of the residual displacing naphtha, amounted to 4.8% of the stock charged, and had an oil content of 0.6% and a melting point of 152 F.

The efllux mother liquor from the first displacement was then chilled to 41 F., charged to a second displacement tower, and the mother liquor was again displaced downwardly from the crystalline wax with 45 parts by volume of special naphtha (based on the volume of the mixture charged) The resulting wax, after removal of the residual displacing naphtha, amounted to 3.44% of the stock charged, and had an oil content of 3.3% and a melting point of 127 F. The final mother liquor, after removal of solvent therefrom by distillation, yielded 91.8% of oil (based on the volume of the stock charged) having a pour test of about 40 F. If it is found desirable to produce oils of,very low pour test, i. e., F..or lower, displacement may be effected in one or more stages at temperatures of the order of 0 F or lower.

In some instances I may dilute the efilux mother liquor from the initial displacement step with additional quantities of solvent prior to subjecting such liquor to further chilling and displacement, in order to maintain the crystalline wax resulting from the chilling at the optimum concentration for displacement.

It will be seen, in accordance with the examples herein given, that by my process I am able to separate a mixture containing hydrocarbons of different fusibility into fractions respectively more fusible, i. e., the oil and/or soft wax,

and less fusible, i. e., the hard wax, in a practical and economical manner not heretofore known.

In addition to the solvents and displacing or wash liquids disclosed hereinabove, there may also be employed the conventional dewaxing solvents such as ketones, alcohols, esters, ethers, halogenated hydrocarbons and liquefied normally gaseous hydrocarbons. The light hydrocarbons such as ethane, propane, butane and pentane and mixtures thereof, are of particular utility in my process, by reason of their very low viscosities and gravities which make them especially desirable as displacing liquids. During the displacement of mother liquor from the wax mass, the compacting of the wax crystals may be greatly reduced and the rate of displacement substantially increased by employing displacing liquids having viscosities of the order of those of the liquefied normally gaseous hydrocarbons.

In operating my process I take advantage of several physical properties which vary through rather wide limits. For example, it has already been pointed out that advantage is taken of differences in specific gravity of mother liquor and displacing liquid respectively to maintain'a horizontal interface therebetween during displacement. If the wax-containing mixture be of such a character that relatively rapid rates of displacement are feasible, it becomes highly desirable to maintain a very considerable gravity differential between mother liquor and displacing liquid, for the reason that, in general, the tendency towards disruption of the interface and/or channeling is greater when relatively high rates of displacement are employed, and gravity differentials of considerable magnitude tend to prevent such disruption orichanneling When, .for. example, ethylene dichloride is employed .inmaking'up the. crystallizing solution or mother liquor. and butane is used as the displacing liquid, itis possible to. obtain a specific Specific Solvent gravity] Ohloroform Carbon tetrachlorid Acetone chloride Pentachloro-ethane. Methylene bromide Acetylene tetra bromide Methylene iodide The relationship between the specific gravity of the mother liquor, the displacing liquor and. the solid wax crystals is of considerable importance in the efficient operation of my process. Wax from some wax-containing stocks, for example, when crystallized from solution produce crystals which are small and soft, and tend to pack in a relatively dense layer against the displacement tower screen, thus requiring the use of excessive pressure to continue the displacement and increasing the danger of channeling of the displacing liquid. In such a case the tendency to pack against the screen may be minimized by employing a crystallizing solvent or mixture of solvents of very high gravity, such as those mentioned above. It will be seen that the higher the gravity of the mother liquor, with respect to the gravity of the wax crystals, the greater will be the buoyant force effective upon the crystals, and this buoyant force will tend to lift the crystals from the screen and therefore reduce the tendency for them to pack against the screen.

Likewise, the situation is somewhat similar with respect to the gravity differential between the wax crystals and the displacing liquid. After the displacement step has proceeded for a time, a portion of the wax mass will consist of washed wax crystals containing displacing liquid. If the displacing liquid (in the case of downward displacement) be of considerably lower specific gravity than that of the crystals, there is a tendency for the washed crystals to settle and pack toward the receding interface of the displacing liquid. If, however, the specific gravity of the displacing liquid be adjusted so that it is equal or even greater than that of the wax crystals, the tendency of the crystals to pack is largely eliminated. The specific gravities of the various waxes usually fall within the range of from about 0.90 to 0.94 at 60 F., although some special waxes or wax fractions may be found within the range of, for example, 0.75 to 0.95 at 60 F. The following values are typical of the specific gravities of waxes obtained from various oil fractions from East Texas crude oil.

Furthermore, the viscosity of the mother liquor and the displacing liquid must also be taken into consideration, for the reason that the average distance between crystals is very small, and the greater the viscosity of the liquid which must pass through these orifices, the greater will be the force required to effect displacement, and the greater will be the compressive forces acting upon the crystals of the wax mass. Therefore, it is particularly desirable to employ displacing liquids of relatively low viscosity, i. e., of the order of 0.1 to 5 centipoises, and preferably of the order of 0.1 to 2.0 centipoises, at the temperature of displacement.

It is to be understood that it is not possible to specify the optimum conditions for displacement, inasmuch as these conditions vary with the different wax-containing stocks to be handled. Thus, if the wax-containing stock is such that the crystals of wax are large and relatively hard, displacement may be carried out at relatively high rates with little concern as to the packing of wax against the screen or to undue compressionof the wax mass. In this case it is advisable to employ as high a gravity differential as is possible in order that the rapidly advancing interface between displacing liquid'and mother liquor may be kept horizontal. If, on the other hand, the crystals are softand apt to pack, it is desirable that a high gravity differential between mother liquor and wax be employed, in order to reduce the tendency of the wax to pack against the screen, and, in addition, thedisplacing liquid is preferably of relatively high gravity to prevent the washed wax from being unduly compacted. In this case, the gravity differential between mother liquor and displacing liquid is somewhat less than that in the preceding instance. It is desirable that the viscosity of both mother liquor and displacing liquid be relatively low, although it may not be possible in every case to employ either the lowest viscosity of mother liquor or the lowest viscosity of displacing liquid, and still retain the desired gravity differential between'the two liquid phases and the wax.

Furthermore, the displacing liquids employed in my process may be saturated with wax, preferably oil-free, prior to their use in the displacing step to reduce solvent power thereof. for wax. Or, the displacing liquid may contain a suspension or dispersion of fine wax particles which will tend to fill incipient cracks or channels which may develop in the wax mass during the displacing operation.

The volume of displacing Or washing liquid employed in removing the mother liquor from the wax mass may be. of the order of from 20% to 100%, or more, by volume of the oil-wax-solvent mixture charged to the displacing tower. The utilization of small volumes of displacing liquid, i. e., less than 100% by volume of the charge, is disclosed and claimed in the co-opending application of J. A. Alexander, Serial No. 4,159, filed January 30, 1935, now Patent No. 2,083,547.

The percent oil in wax, as herein referred to, was determined on the weight percentage basis, in accordance with the following method:

25 gm. of wax (M. P. 120 F. or higher) or 35 gm. of wax (M. P. less than 120 F.) is heated with suficient ethylene dichloride to make up a homogeneous solution ofv approximately 500 cc., and the exact temperature and volume of the solution is noted. This solution is then cooled, with stirring, to a temperature of from 0 F. to 6 F., and the resulting wax slurry is run onto a paper filter and allowed to filter by gravity. A quantity of the filtrate (100 cc.) is placed in a tared evaporating dish, the exact volume and temperature being noted. The ethylene dichloride is then evaporated'oif at a temperature of from F. to F., and any residual solvent is removed by subjecting the heated dish and contents to reduced pressure (25 rn/m.) for a period of 15 minutes. Any ethylene dichloride vapors remaining are then swept out by a current of gaseous carbon dioxide, and the dish is cooled and weighed. From the weight of the oil thus determined, the quantity of'wax taken as a sample, the volume of the solvent employed, temperature and volume corrections being made, the percentage by weight of the oil in the wax may readily be calculated. The method above outlined is considerably more accurate and stringent than the conventional Expressible oil and moisture test known to those skilled in the art. Depending upon the character of the wax, from 1% to 15% or more of oil may be present in the wax and still be undetectable by the latter test.

For brevity, in the appended claims, the terms solvent liquid and displacing liquid are to be understood to comprehend those compounds in which 011 is readily miscible and wax is relatively immiscible at the temperatures employed in the separation of the oil and the wax. Also, the term wax mass as employed herein and in the appended claims, comprehends a porous mass or body of wax crystals containing oil or oil and solvent distributed therethrough.

What I claim is:

1. A process for dewaxing waxy oil which comprises chilling waxy oil to congeal the same and leaching the congealed waxy oil with a solvent which has a relatively high solvent power for the oil but a relatively poor solvent power for the wax, the temperature of leaching being sufficiently low to maintain said wax in a solid condition, said solvent being of a higher specific gravity than said wax and separating said wax from the oil solvent solution.

2. A method as in claim 1 in which the solvent comprises a chlorinated carbon containing compound which has a high solvent power for oil and a low solvent power for wax at low temperatures, said chlorinated carbon containing compound being fluid at the dewaxing temperature and having a specific gravity greater than the specific gravity of the wax desired to be separated from the waxy oil.

3. The process of separating a hydrocarbon oil-wax mixture into solid constituents and liquid constituents, which comprises producing a wax-containing mixture, cooling said mixture to effect crystallization of wax to form. a wax mass containing less than substantially 10% by volume of solid wax and displacing from said Wax mass, withoutsubstantial agitation thereof and under a low differential pressure, the liquid constituents of said mass with a displacing liquid, while maintaining a substantially horizontal interfacebetween said displacing liquid and the liquid constituents being displaced.

4. The process. of separating a hydrocarbon oil-wax mixture into; solid constituents and liquid constituents, which comprises producing a taining a substantially horizontal interface be-.

tween said displacing liquid and the liquid constituents being displaced.

5. The process of separating a hydrocarbon oil-wax mixture into solid constituents and liquid constituents, which comprises diluting said mixture with a solvent liquid, cooling the diluted mixture to effect crystallization of wax to form a wax mass containing less than substantially 10% by volume of solid wax and displacing from said wax mass, without substantial agitation thereof and under a low differential pressure, the liquid constituents of said mass with a displacing liquid, while maintaining a substantially horizontal interface between said displacing liquid and the liquid constituents being displaced.

6. The process of separating a hydrocarbon oil-wax mixture into solid constituents and liquid constituents, which comprises producing a wax-containing mixture, cooling said mixture to effect crystallization of wax to form a wax mass containing less than substantially 10% by volume of solid wax and displacing from said wax mass, without substantial agitation thereof and under a differential pressure of less than substantially 5 lbs/sq. in. per one foot depth of mass, the liquid constituents of said mass with a displacing liquid, While maintaining a substantially horizontal interface between said displacing liquid and the liquid constituents being displaced.

'7. The process of separating a hydrocarbon oily wax mixture into solid constituents and liquid constituents, which comprises producing a wax-containing mixture, cooling said mixture to effect crystallization of wax to form a wax mass containing from about 1% to about 6% by volume of solid wax and displacing from said wax mass, without substantial agitation thereof and under a diiferential pressure of less than substantially 5 lbs/sq. in. per one foot depth of mass, the liquid constituents of said mass with a displacing liquid, while maintaining a substantially horizontal interface between said displacing liquid and the liquid constituents being displaced.

8. The process of separating a hydrocarbon oil-wax mixture into solid constituents and liquid constituents, which comprises producing a wax-containing mixture, cooling said mixture to effect crystallization of wax to form a wax mass containing from about 2.5% to about 4.5% by volume of solid wax and displacing from said wax mass, without substantial agitation thereof and under a differential pressure of less than 5 lbs/sq. in. per one foot depth of mass, the liquid constituents of said mass with a displacing liquid, while maintaining a substantially horizontal interface between said displacing liquid and the liquid constituents being displaced.

9. The process of separating a hydrocarbon oil-wax mixture into solid constituents and liquid constituents, which comprises producing a wax-containing mixture, cooling said mixture to effect crystallization of at least a portion of the wax, said crystalline wax being less than substantially 10% by volume of the mixture, forming the crystalline Wax into a wax mass of substantial uniformity and containing the major portion of the liquid constituents of the mixture distributed therethrough, and displacing from said mass, wthout substantial agitation thereof and under a low differential pressure, the liquid constituents of said mass with a displacing liquid, while maintaining a substantially horizontal interface between said displacing liquid and the liquid constituents being displaced.

SEYMOUR W. FERRIS. 

